Earnings Per Share (Computation Of Basic And Diluted Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 54,608	$ 53,115	$ 50,041	$ 49,111	$ 35,512	$ 38,355	$ 43,831	$ 39,052	$ 206,875	$ 156,749	$ 151,398
Less: Preferred stock dividends	3,629	3,628	3,628	3,628	3,629	4,079	1,580	1,581	14,513	10,869	6,323
Net income applicable to common shares—Basic	$ 50,979	$ 49,487	$ 46,413	$ 45,483	$ 31,883	$ 34,276	$ 42,251	$ 37,471	192,362	145,880	145,075
Add: Dividends on convertible preferred stock, if dilutive									6,313	6,314	6,323
Net income applicable to common shares—Diluted									$ 198,675	$ 152,194	$ 151,398
Weighted average common shares outstanding (in shares)									50,278	47,838	46,524
Common stock equivalents (in shares)									894	1,029	1,246
Convertible preferred stock, if dilutive (in shares)									3,100	3,070	3,075
Total dilutive potential common shares (in shares)									3,994	4,099	4,321
Weighted average common shares and effect of dilutive potential common shares (in shares)									54,272	51,937	50,845
Net income per common share - Basic (usd per share)	$ 0.98	$ 0.96	$ 0.94	$ 0.94	$ 0.66	$ 0.71	$ 0.89	$ 0.79	$ 3.83	$ 3.05	$ 3.12
Net income per common share - Diluted (usd per share)	$ 0.94	$ 0.92	$ 0.90	$ 0.90	$ 0.64	$ 0.69	$ 0.85	$ 0.76	$ 3.66	$ 2.93	$ 2.98